In an x-ray tube, electrons can emit from an electron-emitter to an anode. A material in or on the anode can form x-rays in response to impinging electrons from the electron-emitter. An x-ray tube with a thermionic electron-emitter must expend a substantial amount of energy to heat the electron-emitter. This energy for heating the electron-emitter can be costly and can place an added burden on the energy source. It would be beneficial to reduce the required energy input to an x-ray tube.
Another problem of thermionic electron-emitters is evaporation of the filament because of its high temperature. Consequently, filament life can be reduced. Also, the evaporated metal from the filament can coat the x-ray tube in undesirable locations, and can create an electrically conductive path between the anode and the filament, resulting in degraded x-ray tube operation and/or early failure.
It is sometimes desirable to insert an x-ray tube into a small space. Because of large voltage differentials between the electron-emitter and the anode, it can be difficult to manufacture small x-ray tubes. It would be beneficial to provide an x-ray tube that can have a small size.